1. Field of the Invention
The present invention relates to a display control technique for a rear-projection type display apparatus.
2. Description of the Related Art
A variety of high-quality video sources are available, including video sources such as high-definition television (HDTV) broadcasting. In addition, presentations and the like in meeting rooms are generally conducted with videos on computers. For this reason, increasing demands have arisen for improvement in the image quality of video apparatuses and increases in the screen sizes of the apparatuses used for such purposes. A rear-projection type display apparatus is available as a promising technology for implementing such a high-quality, large-screen display apparatus.
An apparatus designed to project videos by using a high-luminance CRT (Cathode-Ray Tube) had initially been the mainstream of rear-projection type video apparatuses. Recently, however, a rear-projection type video apparatus using a light valve such as a transmissive liquid crystal, a reflective liquid crystal or a digital micro-mirror device (DMD) has become the mainstream. Such an apparatus is designed to apply light to the light valve and enlarge/project video light from an image surface of the light valve onto the screen by using the projection optical system. Many such apparatuses use, as light valves, LCOS (Liquid Crystal On Silicon) panels having characteristics that inter-pixel joints are inconspicuous and the optical control efficiency is high. Note that an LCOS panel is a reflective liquid crystal panel obtained by forming a liquid crystal layer on a semiconductor substrate. This apparatus uses, as a light source, a discharge lamp such as a superhigh pressure mercury lamp or a metal halide lamp owing to its high luminous efficacy.
In general, a discharge lamp as the above light source decreases in luminance level along with operating time. This is caused by a phenomenon called blackening in which the metal of the lamp electrode evaporates, deposits on a portion of the inner surface of the glass of the lamp, and blackens, or a phenomenon called “being devitrified” in which the glass is vitrified by ultraviolet light or the like to become opaque. In addition, the vapor amount of mercury in the lamp changes every moment until a predetermined period of time has elapsed after the start of lighting. For this reason, in this period, the emission spectrum of the lamp changes, resulting in changes in luminance, white balance, and the like. Furthermore, in the liquid crystal panel, for example, the transmission property of the liquid crystal changes due to a change in temperature or the like, resulting in poor white balance and the like.
In order to solve these problems, there have been proposed several methods of detecting projected light and correcting luminance, white balance, and the like. For example, Japanese Patent Laid-Open No. 08-292407 discloses a technology for condensing light from a transmissive liquid crystal panel and providing a sensor on an outer periphery of the aperture portion of a stop provided at the focal point of the light. Providing the sensor at the outer periphery of the aperture portion makes it possible to identify a change in the scattering property of the liquid crystal panel without any influence on the display of the screen. Japanese Patent Laid-Open No. 11-242293 discloses an arrangement for a rear-projection type display apparatus, which has a projection range set in advance to be larger than the screen, and includes sensors arranged on the respective sides of a screen holder (outer peripheral portion) so as not to protrude outside the display portion. In addition, Japanese Patent Laid-Open No. 2003-174651 discloses an arrangement for detecting weak light over a reflecting mirror.
In a light valve, in addition to changes in transmittance with changes in temperature, fluctuations in transmittance may occur depending on the display position on a frame due to variations in cell gaps in the liquid crystal cells even if the same driving voltage is applied. This causes luminance inconsistency in a video projected on the screen. Many apparatuses designed for high-resolution image display have an arrangement which includes liquid crystal panels for the respective colors, i.e., red (R), green (G), and blue (B), and independently controls the panels for the respective colors. In the case of such a three-panel arrangement, if each panel has the above luminance inconsistency, color inconsistency occurs depending on the display position on a frame.
The above prior art, however, detects only light at a portion which is not displayed on the display unit, i.e., part of light. This makes it impossible to measure and correct overall inconsistency on a frame or the like. In addition, sensors are provided around the screen on the assumption that enlarged displacement and the like are performed, and there is a portion which is not displayed on the displayed unit. That is, it is necessary to perform so-called over scanning. However, when a PC frame or the like is to be performed, it is necessary to display the entire frame within the screen. Thus, it is impossible to perform over scanning, resulting in incapability of detection.